This invention relates to a magnetic resonance (MR) scanner apparatus. More specifically, this invention relates to a mobile, hydraulically-operated table useful with an MR scanner for transporting a patient from a preparation room to an MR examination room, and for retrievably positioning the patient within the bore of a scanner magnet.
The magnetic resonance phenomenon has been utilized in the past in high resolution MR spectroscopy instruments by structural chemists to analyze the structure of chemical compositions. More recently, MR has been developed as a medical diagnostic modality having application in imaging the anatomy, as well as in performing in vivo, non-invasive, spectroscopic analysis. As is now well known, the MR resonance phenomenon can be excited within a sample object, such as a human patient, positioned in a homogeneous polarizing magnetic field, by irradiating the object with radio frequency (RF) energy at the Larmor frequency. In medical diagnostic applications, this is typically accomplished by positioning the patient to be examined in the field of an RF coil having a cylindrical geometry, and energizing the RF coil with an RF power amplifier. Upon cessation of the RF excitation, the same or a different RF coil is used to detect the MR signals emanating from the patient volume lying within the field of the RF coil. The MR signal is usually observed in the presence of linear magnetic field gradients used to encode spatial information into the signal. In the course of a complete MR scan, a plurality of MR signals are typically observed. The signals are used to derive MR imaging or spectroscopic information about the object studied.
A whole-body MR scanner used as a medical diagnostic device includes a magnet, frequently of solenoidal design, to produce the polarizing magnetic field. The bore of the magnet is made sufficiently large to accommodate RF, gradient, and shim coil assemblies, as well as the torso of a patient to be examined. The scanner also includes a table which supports a cradle used to retrievably position the patient within the bore of the magnet. The table is aligned longitudinally with the bore of the magnet and disposed at the same height to facilitate the advancement of the cradle between a home position when the cradle is on the table and an advanced position when the cradle is in the magnet. A bridge structure in the bore supports the cradle and the patient when the cradle is in the advanced position.
It is desirable in an MR scanner apparatus to construct a table which is detachable from the magnet and which is mobile. The height of the table should be capable of adjustment to facilitate transfers of the patient from a gurney onto the cradle and to facilitate the movement of the cradle into and out of the magnet bore during an MR examination. A mobile table is desirable to, for example, promote efficient use of the scanner in that while one patient is undergoing examination, another could be readied in the preparation room. A mobile table is advantageous in situations where it is necessary to remove a patient from the magnet (as in an emergency) and to transport the patient with minimum delay to an area where assistance in the form of support equipment and care is available. It will be recognized that, due to the strong magnetic field (typically 1.5 tesla), support equipment must be located away from the magnet. This is necessary not only to ensure that the magnetic field does not adversely affect equipment operation, but to avoid magnetic objects in the vicinity of the magnet which could be drawn by the magnetic field toward the magnet. It will be further recognized that magnetic objects near the magnet may disturb the homogeneity of the field which could render the data collected unsuitable for use.
It is believed that, in the past, mobile tables have been used with computerized tomography (CT) apparatus. Such tables, however, are not suitable for use with MR scanner systems due in great part to the highly magnetic environment associated with MR. For example, the table must be constructed from non-magnetic materials. This requirement eliminates electric motors as energy sources to adjust table height. An alternative is to employ hydraulics as the power medium. Conventional hydraulic principles, however, cannot be easily implemented. One problem is the difficulty in transferring and storing energy in the mobile table because conventional hydraulic connectors have a tendency to leak when connected and disconnected repeatedly.
Another problem which must be addressed in a mobile MR table is that a docking device must be provided for aligning and holding the table in position while the patient is transferred into and out of the magnet in the course of an MR examination. Conventional proposals employed a long dock extension to ensure alignment of the cradle during transfer. This extension increased the size of the RF shield room used to provide bidirectional attenuation of RF energy and was bulky and inconvenient to use. Another factor which must be considered is the requirement to undock the table in the event of an emergency.
In a mobile table there is also the need to monitor table operational parameters such as positive docking of the table to the magnet, and hydraulic pressure. These functions must be accomplished without electrical connections between the table and the magnet.
It is an object of the invention to provide means for transferring hydraulic energy to a mobile table, which is part of an MR scanner, without utilizing conventional hydraulic connections.
It is a further object of the invention to provide means for monitoring operational parameters in a table of an MR scanner without employing electrical connections between the table and magnet.
It is still another object of the invention to provide a docking mechanism for securing a table to a magnet of an MR scanner.